Whitefly-transmitted geminiviruses are emergent pathogens in the Caribbean Region, including Puerto Rico, and Central America. Increased economic importance of begomovirus pathogens is attributed to the invasion by a polyphagous, exotic, Old World whitefly vector, Bemisia tabaci type B, and to the expansion of irrigated agriculture. Recent evidence suggests that the B type vector is capable of displacing New World B. tabaci in the region, and that it may also be a more effective vector of certain begomoviruses. Collectively, these changes have resulted in the emergence of begomoviruses that infect many species within a large number of plant families in the Caribbean, though neither the precise origin nor the pedigree of these emergent viruses is well understood. Begomovirus Cp sequences and two Cp fragments were assessed for their utility in establishing the provisional identity and classification of field isolates. Consistent with elucidating the dynamics underlying begomovirus-vector-host interactions that promote, discourage, or delimit the emergence of strains/viruses, non-coding sequences involved in replication and other viral ORFs are also under investigation. Their analysis will permit the reconstruction of gene trees, and/or facilitate predictions about formation of viable reassortants that may utilize replication-, movement-, and/or transmission-specific sequences that feasibly influence virus evolution.

In field tests conducted at Starkville, MS during 1996 and 1997, Cochliobolus sativus was most frequently isolated, and Fusarium acuminatum was the most prevalent Fusarium spp. from crown and root tissues of cv. Wakefield wheat seedlings. Cochlioblus spicifer, Embellisia chamydospora and Microdochium bolleyi were also consistently associated with wheat seedlings. Pathogenicity tests were conducted with three isolates each of C. spicifer, E. chlamydospora and M. bolleyi in test tube culture and two isolates each of C. spicifer, E. chlamydospora and M. bolleyi under greenhouse conditions. Seedlings infected with E. chlamydospora and M. bolleyi had slight to moderate orange to light-brown discoloration of crown and seminal roots in test tubes. Cochliobolus spicifer induced preemergence damping-off, black root discoloration and root pruning, and reduced seedling emergence, root fresh weight and shoot dry weight. In the greenhouse, M. bolleyi and E. chlamydospora reduced shoot dry weight, fresh and dry weight of roots, and plant emergence. Cochliobolus spicifer reduced seedling growth rate. This constitutes the first report of pathogenicity of these fungi to wheat seedlings on the Upper Coastal Plain Land Resource Area of Mississippi.

A total of 51 Phytophthora capsici isolates from field samples were screened for sensitivity to Ridomil Gold EC (R) -2-[2,6-dimethylphenyl)-methoxyacetylamino]-propionic acid methyl ester). These isolates are from watermelon (14), tomato (7), yellow squash (6), squash (6), pepper (6), zucchini (4), cantaloupe (3), cucumber (3), and eggplant (2). Ridomil Gold EC was incorporated into corn meal agar (CMA) to give final concentrations of 0, 10, 100 ppm. Four 5.0 mm plugs taken from a three day old culture grown on CMA were placed on the center of each quadrant of duplicate plates at each concentration. Colony diameter was measured after 3 days growth at 28C. Isolates were considered to be insensitive if growth was greater than 40% of the control. Of the 51 isolates tested, 40 isolates were sensitive to both concentrations. Seven isolates were insensitive only at the 10 ppm, where as 5 isolates were insensitive at 100 ppm. Among the five insensitive isolates, two were from yellow squash and one each from tomato, pepper, and zucchini.

Fungicides, including azoxystrobin (Heritage; 600 mg/L), fludioxonil (Medallion; 75 mg/L), thiophanate methyl (SysTec 1998; 2.6 ml/L), thiophanate methyl+chlorothalonil (Consyst; 1.8g/L), thiophanate methyl+etridiazole (Banrot 40 WP; 674 mg/L), a bicarbonate fungicide (Armicarb 300; 5.0 g/L), and mefenoxam (Subdue Maxx; 156 µl/L) were evaluated for reduction of Fusarium solani and Pythium sp. in tubers of caladium 'Frieda Hemple'. All were used in combination with a standard hot water treatment (50°C/30 min), and all except Armicarb 300 and Banrot were used alone and in combination with mefenoxam. Infection incidence and severity were assessed by placing tuber cores on Fusarium and Pythium selective media. Pythium was not detected in any tubers. Fusarium incidence was significantly reduced by Banrot, Armicarb 300, Consyst, and Heritage, but not by hot water alone, Medallion, SysTec 1998, or Subdue Maxx. Although the severity of Fusarium infection was reduced by hot water alone, all fungicides in combination with hot water were significantly more effective.

Evaluation of fungicides for control of lychee anthracnose. McMillan, Robert T., Jr. University of Florida, IFAS, Tropical Research and Education Center, Homestead, FL 33031. Publication no. P-2000-0007-CRA.

Lychee (Litchi chinensis 'Mauritius') is highly susceptible to Colletotrichum gloeosporioides Penz. in Miami-Dade County Florida. Fungicides were applied to four single tree plots arranged in a randomized complete block design in a 4-year-old grove planted on a 20 × 25 foot spacing. Applications were made with a handgun sprayer at 200 lb/in.(^2) of pressure using approximately 0.75 gallons per tree. Dithane M45 alone and in combination with Benlate were applied weekly until 14 days before harvest. All treatments gave significant control of lychee anthracnose. Folicur alone and Folicur-Dithane provided the best lychee anthracnose control. Dithane alone significantly reduced anthracnose over the untreated control. None of the fungicides tested caused injury to the fruits or leaves.

Pathogenicity of Rhizopycnis vagum on melon roots. M. E. MILLER (1), X. Y. Zheng (1), B. D. Bruton (2), and D. F. Farr (3). (1) Texas A&M University, Weslaco, TX 78596; (2) USDA-ARS, Lane, OK 74555; (3) USDA-APHIS, Beltsville, MD 20705. Publication no. P-2000-0008-CRA. Rhizopycnis vagum was isolated from 13-32% of roots of 8 week old cantaloupe ('Magnum 45'), honeydew ('Honey Brew' and 'Morning Ice'), and watermelon ('Jubilee II') plants from a field with a history of vine decline disease of unknown etiology. The isolation frequency of this species, made from subsequent, biweekly isolations, was similar through plant maturity. R. vagum has also been isolated from roots of melon plants exhibiting vine decline symptoms in Guatemala and Honduras. 'Jubilee' watermelon and 'Caravelle' cantaloupe plants inoculated with 1,600, 3,200, and 6,400 CFUs/g of soil had a significant reduction (p=0.05) in vine length and vine dry weight over untreated controls. Inoculated 'Jubilee' watermelon plants also had significantly higher root disease ratings and lower root dry weights. These data indicate that R. vagum is pathogenic on melon, thus, it may be involved either alone or in combination with other pathogens in melon vine decline disease in Texas and other areas.

TYLCV is the main constrain for tomato production in Dominican Republic (D.R.). Management strategies include the utlization of TYLCV-tolerant cultivars. A field study was conducted in Azua, D. R., to determine the extent of tolerance of 25 processing tomato cultivars to TYLCV. Cultivars were transplanted in a randomized block design with three replications, and managed according to local practices. No control of TYLCV vectors was performed, to allow for natural infection. Measured variables were: amount of Bemisia spp/leaflet, TYLCV incidence and severity (%), and crop yield. Cultivars 'Gem Pride', HA-3102, HA-3106, HA-3108 and HA-3118 did not present TYLCV symptoms, and had the highest yields. APT-391, F7332, 'Marina', 'Veronica', APT-268, 'Topspin', 'Yaqui' and IDIAP-T7 had TYLCV incidence below 20% by 34 days after transplanting (DAT). SUN-6200, SUN-6117, SUN-6235, SUN-6109, 'Tarim', 'Mingo', 'Fame', 'Bright Pearl' and Farmers-209 had incidence and severity above 30% by 34 DAT. The highest incidence at that time was 75% in 'Tarim'.

Isolates of Rhizoctonia spp., causing brown patch of turf, were collected from several golf courses in the US where azoxystrobin had never been used. The sensitivity of these isolates to azoxystrobin was evaluated using a perennial ryegrass (Lolium perenne) bioassay. For this assay, turf was grown in 4 × 4 inch pots. Two weeks after planting, turf was sprayed with azoxystrobin at 10, 3, 1, 0.3, 0.1 or 0 µg/mL. Twenty-four hours after fungicide application, turf was inoculated by placing four Rhizoctonia-colonized ryeberries onto the center soil surface of each pot. The percentage of turf area infected was assessed 4 days after inoculation and ED(50) values were calculated. To validate the reliability of this test, the assay was repeated six times using three of the isolates. Based on the evaluation of 27 isolates, the ED(50) values (µg/mL) relative to the percentage of turf area infected ranged from 0.243 to 1.868, with a median value of 0.843. Baseline information will be useful for future monitoring and early detection of shifts in sensitivity to azoxystrobin.

A series of studies were conducted to evaluate the efficacy of Abamectin (Agri-Mek 0.15EC) against the root-knot nematode (Meloidogyne incognita) on tomato. Under greenhouse conditions, Agri-Mek at rates as low as 0.01 ppm completely prevented nematode penetration of tomato roots. Under field conditions, Agri-Mek applied as a drip treatment reduced nematode galling, increased yields and reduced nematode population densities. Weekly or biweekly applications at rates ranging from 113.5 to 567.5 g a.i./ha were effective.

The application of biotechnology, a technology utilizing genetically modified cells or microorganisms, has created new possibilities for virus research and has allowed virologists to answer questions that were not addressed by previous technologies. The cloning and sequencing of viral genomes has led to advances in viral taxonomy and in the identification of viral genes and their functions. Biotechnology has presented more sensitive and rapid diagnostic techniques. Current areas of research utilizing biotechnology are the elucidation of virus movement and the identification and characterization of host gene products which are mobilized or sequestered for virus replication. The identification of host defense mechanisms and the viral genes which suppress them are other areas of research utilizing biotechnology. Such studies will increase our understating of viral pathogenesis. This knowledge plus that of viral gene functions are being used to create plants with resistance to viruses through approaches such as pathogen­derived resistance or activation of host defense mechanisms.

Activities of soil enzymes have been correlated with general microbial activity, biocontrol of soilborne plant pathogens, and soil fertility status. Nutrient cycling, chitinolytic activity, aerobic, and general microbial populations can be measured indirectly through enzymatic activity. Agronomic practices, which include cropping systems, tillage, and fertilization, have an impact on soil microbial activity, which can be measured through soil enzyme analysis. A short-term study of intercropping of maize (Zea mays L.) and jackbean (Canavalia ensiformis (L.) DC.) in Chiapas, Mexico, was conducted in 1995-97. Several interactions among cropping systems, tillage, and fertilization on the activities of catalase, esterase, chitobiase, and urease were determined. Results indicated that maize produced with sustainable practices in tropical regions increased microbial activities and possibly suppressiveness to soilborne plant pathogens.

Soil enzymatic activity has been correlated with microbial activity and suppressiveness to soilborne plant pathogens. A microplot study in Auburn, Alabama, conducted in 1998 demonstrated significant differential enzymatic activities between the rhizospheric soils of tropical legumes in the genera Canavalia, Mucuna, Indigofera, Crotalaria, Glycine, and Clitoria and the rhizospheric soils of cotton and sorghum. Results also showed that the rhizosphere effects of legumes greatly modify both plant pathogenic and free-living nematode populations. These results confirm previous findings indicating that some legumes can be used in crop rotation systems under the subtropical conditions of Alabama, to suppress nematode pests of crops such as sorghum and cotton, and improve soil fertility status.

Saw palmetto, a palm species, grows naturally in the southeastern coastal plain of the United States and is most abundant in Florida. Extracts from saw palmetto fruits are sold in the world health supplement market at a value of $2 billion. In 1996 and 1997, a high incidence of sunken fruit lesions and a premature fruit drop were observed in natural field plots that were located in 4 counties in central and southern Florida. Fruit loss ranged from 50-100% from June to August 1997. A fungus isolated from diseased fruiting spadices and saw palmetto fruit was tentatively identified as Colletotrichum gloeosporiodes based upon morphological characteristics. Inoculation of saw palmettos spadices resulted in typical disease symptoms and fruit abscission. A morphologically identical fungus was reisolated in fulfillment of Koch's postulates confirming its role as the causal agent.

Insects were collected from pepper plantations where bacterial spot disease caused by Xanthomonas campestris pv. Vesicatoria (Xcv) occurs to examine their role as bacterial vectors. The insects were: the pepper weevil (Anthonomus eugenii), the sweet potato whitefly (Bemisia tabaci) and a fly (Fam. Chloropidae). Bacteria from the external surface and inner body of the insects were isolated using nutrient agar and broth at 28°C. Bacteria isolated from the pepper weevil and the dipteran were classified using the Biolog(^R) computer system. The genus and/or the species isolated from the pepper weevil were: Enterobacter sp., E. agglomerans, Corynebacterium aquaticum, y Kingella denitrificans. The bacterial isolated from the dipteran were: Enterobacter agglomerans, E. cloacae, Corynebacterium aquaticum, C. pilosum, Flavobacterium gleum, Leuconostoc mesenteroides, and Weeksella zoohelcum. Bacteria isolated from the whitefly were not identified. Some bacteria isolated from the insects were pathogenic on pepper fruits under greenhouse and in vitro conditions. Xcv was not detected in our study.

Most fungi contain viruses, yet very little is known about their effect of the biology of their hosts. Only a few viruses of fungi have been well characterized, and in each of these cases, the virus has been found to profoundly affect its host, often in ways that can be used for biological control of the host. The best studied use of fungal viruses for biological control is that of hypovirulence of the chestnut blight pathogen, Cryphonectria parasitica. The virus responsible for hypovirulence of this fungus was discovered because of its effectiveness in controlling this very serious tree disease. The virus has been characterized and the molecular basis of its ability to cause hypovirulence is being studied. Study of this virus-host relationship is revealing many previously unknown aspects of the biology of the fungus, thus contributing to our understanding of developmental processes in fungi. It is anticipated that similar studies of other putative hypovirulence-causing viruses of fungi will likewise prove to be fruitful.

The techniques of nucleic acid hybridization (NAH) and polymerase chain reaction (PCR) are used for the detection of phytopathogens. These applications share similar characteristics of specificity, sensitivity, rapidity and reliability. We describe the standardization of parameters for the evaluation of PCR and NAH for the detection of two begomoviruses: Havana tomato virus (HTV) and tomato yellow leaf curl virus (TYLCV­Isr) which infect tomato in Cuba. The results demonstrated the feasibility of specific detection using probes and primers from the common region of HTV and TYLCV. Both techniques were useful for detection, and showed a sensitivity greater than 90% with an upper limit of detection of 25 fg for PCR and 100 ­160 pg for NAH. PCR specificity was reduced due to the appearance of false positives. NAH was the preferred technique for the large scale detection of these viruses in the tomato improvement program in Cuba.